Methods of forming semiconductor devices with metal silicide using pre-amorphization implants and devices so formed

ABSTRACT

A method of forming a semiconductor device can be provided by forming an opening that exposes a surface of an elevated source/drain region. The size of the opening can be reduced and a pre-amorphization implant (PAI) can be performed into the elevated source/drain region, through the opening, to form an amorphized portion of the elevated source/drain region. A metal-silicide can be formed from a metal and the amorphized portion.

This application claims priority from Korean Patent Application No.10-2012-0055543 filed on May 24, 2012 in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein byreference in its entirety.

BACKGROUND

The present invention relates to semiconductor devices and particularlyto devices utilizing metal silicide and methods of fabricating the same.As the integration density of semiconductor devices is scaled to 20 nmor less, the interfacial resistance between a metal silicide and siliconmay be reduced. This is because the interfacial resistance between themetal silicide and the silicon can act as a dominant component ofparasitic resistance of the semiconductor devices.

For example, the interfacial resistance can be reduced by increasing thedoping concentration of a source/drain or reducing the schottky barrierheight. Also, the interfacial resistance can be reduced by increasingthe interface area between the metal silicide and the silicon.

SUMMARY

Embodiments according to the invention can provide method of formingsemiconductor devices with metal silicide using pre-amorphizationimplants and devices so formed. Pursuant to these embodiments, a methodof forming a semiconductor device can be provided by forming an openingthat exposes a surface of an elevated source/drain region. The size ofthe opening can be reduced and a pre-amorphization implant (PAI) can beperformed into the elevated source/drain region, through the opening, toform an amorphized portion of the elevated source/drain region. Ametal-silicide can be formed from a metal and the amorphized portion.

In some embodiments according to the invention, performing the PAI caninclude forming the amorphized portion to include a PAI lower profilethat is remote from the surface, the PAI lower profile having a curvedcross-section. In some embodiments according to the invention, a centralportion of the curved cross-section is curved.

In some embodiments according to the invention, forming themetal-silicide can be provided by forming the metal-silicide to includea silicide lower profile that is remote from the surface, the silicidelower profile having a curved cross-section. In some embodimentsaccording to the invention, a central portion of the curvedcross-section is curved.

In some embodiments according to the invention, forming themetal-silicide can be provided by forming the silicide lower profile ata level that is equal to or higher than a gate oxide layer included in agate structure that is directly adjacent to the elevated source/drainregion. In some embodiments according to the invention, the level isabout 15 nm or less.

In some embodiments according to the invention, forming themetal-silicide can be provided by forming the silicide lower profile ata level that is elevated above a level of a channel region associatedwith at least one directly adjacent gate structure. In some embodimentsaccording to the invention, a depth of the silicide lower profile in theelevated source/drain region is more than one half of a total thicknessof the elevated source/drain region.

In some embodiments according to the invention, reducing a size of theopening can be provided by reducing the size of the opening at a bottomof the opening. In some embodiments according to the invention, reducinga size of the opening can be provided by changing a shape at a bottom ofthe opening to provide curved side walls that curve at the bottom towardthe surface of the elevated source/drain region.

In some embodiments according to the invention, reducing the size of theopening can be provided by etching the surface of the elevatedsource/drain region to recess a level of the surface. In someembodiments according to the invention, reducing the size of the openingcan be provided by RF etching the elevated source/drain region and sidewalls of the opening.

In some embodiments according to the invention, performing the PAI canbe provided by forming the amorphized portion to include a PAI lowerprofile that is remote from the surface, the PAI lower profile having acurved cross-section. In some embodiments according to the invention,the metal-silicide can include an upper recess having a bottom and aside wall, where the bottom is separated from a bottom of the silicidelower profile by a distance that is greater than a distance by which theside wall of the recess is separated from a side wall of the silicidelower profile.

In some embodiments according to the invention, the metal-silicidefurther includes a convex shaped top, opposite the silicide lowerprofile. In some embodiments according to the invention, performing thePAI can be provided by implanting Xe into the elevated source/drainregion to form the amorphized portion including the PAI lower profile,the amorphized portion having a total thickness of at least about 100Angstroms.

In some embodiments according to the invention, performing the PAI canbe provided by implanting Si into the elevated source/drain region toform the amorphized portion including the PAI lower profile, theamorphized portion having a total thickness of at least about 100Angstroms.

In some embodiments according to the invention, a method of forming asemiconductor device can be provided by forming an opening that exposesa surface of an elevated source/drain region. A pre-amorphizationimplant (PAI) can be performed into the elevated source/drain region,through the opening, to form an amorphized portion of the elevatedsource/drain region and a metal-silicide can be formed from a metal andthe amorphized portion.

In some embodiments according to the invention, a semiconductor devicecan include a substrate including a PMOS region and an NMOS region. Afirst contact hole can be in an insulating layer exposing a firstelevated source/drain region in the PMOS region. A first metal contactcan be in the first contact hole on the first elevated source/drainregion. A first metal-silicide can be in the first elevated source/drainregion in contact with the first metal contact, the first metal-silicideincluding a first silicide lower profile that is remote from a surfaceof the first elevated source/drain region, the first silicide lowerprofile having a curved cross-section and the first metal-silicideincluding a planar top portion opposite the first silicide lowerprofile. A second contact hole can be in the insulating layer exposing asecond elevated source/drain region in the NMOS region and a secondmetal contact can be in the second contact hole on the second elevatedsource/drain region. A second metal-silicide can be in the secondelevated source/drain region in contact with the second metal contact,the second metal-silicide including a second silicide lower profile thatis remote from a surface of the second elevated source/drain region, thesecond silicide lower profile having a curved cross-section and thesecond metal-silicide including a convex top portion opposite the secondsilicide lower profile.

In some embodiments according to the invention, a method of forming asemiconductor device can be provided by forming an opening that exposesa surface of an elevated source/drain region. The elevated source/drainregion can be processed to provide an anisotropic metal diffusion ratewithin the elevated source/drain region and a metal-silicide can beformed from a metal and the amorphized portion, according to theanisotropic metal diffusion rate, to provide the metal-silicide toinclude a silicide lower profile that is remote from the surface, thesilicide lower profile having a curved cross-section.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a semiconductor device in someembodiments according to the present invention.

FIG. 2A is a perspective view of a metal silicide shown in FIG. 1.

FIG. 2B is a cross-sectional view of the metal silicide shown in FIG.2A.

FIG. 3 is a cross-sectional view of a semiconductor device in someembodiments according to the present invention.

FIG. 4A is a perspective view of a metal silicide shown in FIG. 3.

FIG. 4B is a cross-sectional view of the metal silicide shown in FIG.4.A.

FIG. 5 is a cross-sectional view of a semiconductor device in someembodiments according to the present invention.

FIG. 6A is a perspective view of a metal silicide shown in FIG. 5.

FIG. 6B is a cross-sectional view of the metal silicide shown in FIG.6A.

FIG. 7 is a cross-sectional view of a semiconductor device in someembodiments according to the present invention.

FIG. 8 is a cross-sectional view of a semiconductor device in someembodiments according to the present invention.

FIGS. 9 and 10 are, respectively, a circuit diagram and a layout view ofa semiconductor device in some embodiments according to the presentinvention.

FIGS. 11 through 16B are cross-sectional views illustrating methods offabricating semiconductor devices in some embodiments according to thepresent invention.

FIG. 17 is a graph illustrating A-Si thicknesses vs. metal silicidethicknesses for different implants.

DESCRIPTION OF EMBODIMENTS ACCORDING TO THE INVENTION

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied indifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fillyconvey the scope of the invention to those skilled in the art. The samereference numbers indicate the same components throughout thespecification. In the attached figures, the thickness of layers andregions is exaggerated for clarity.

It will also be understood that when a layer is referred to as being“on” another layer or substrate, it can be directly on the other layeror substrate, or intervening layers may also be present. In contrast,when an element is referred to as being “directly on” another element,there are no intervening elements present.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the exemplary term “below” can encompass both anorientation of above and below. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. It is noted that the use of anyand all examples, or exemplary terms provided herein is intended merelyto better illuminate the invention and is not a limitation on the scopeof the invention unless otherwise specified. Further, unless definedotherwise, all terms defined in generally used dictionaries may not beoverly interpreted.

The present invention will be described with reference to perspectiveviews, cross-sectional views, and/or plan views, in which preferredembodiments of the invention are shown. Thus, the profile of anexemplary view may be modified according to manufacturing techniquesand/or allowances. That is, the embodiments of the invention are notintended to limit the scope of the present invention but cover allchanges and modifications that can be caused due to a change inmanufacturing process. Thus, regions shown in the drawings areillustrated in schematic form and the shapes of the regions arepresented simply by way of illustration and not as a limitation.

Further, the term “cone” or “reverse cone” is used herein to describethe general shapes associated with, for example, amorphized regions andthe metal silicide regions formed from the amorphized regions. It willbe understood, however, that the term “cone” is not limited to theexplicit mathematical or geometric definition of a cone, but rather isused in a general sense to describe the overall shape of thepre-amorphized implant regions and metal silicide regions, so that theactual structures and regions formed may not necessarily conform to theexact mathematical or geometric definition of a cone. Further, it willbe understood that such regions that are described as being “cone”shaped, such as the amorphized portion of the elevated source/drainregion or the metal silicide formed therefrom, can have a lower profile,that is remote from the surface of an area in which the region isformed, so that the lower profile has a curved cross-section.

FIG. 1 is a cross-sectional view of a semiconductor device 1 accordingto an embodiment of the present invention. FIGS. 2A and B are aperspective view and a cross-sectional view of the metal silicide 151shown in FIG. 1. Referring to FIG. 1, the semiconductor device 1 mayinclude a substrate 100, gates 116, an elevated source/drain 117, afirst interlayer insulating film 121, a second interlayer insulatingfilm 122, a metal silicide 151, and a metal contact 160.

The substrate 100 may be a silicon substrate, a gallium arsenidesubstrate, a silicon germanium substrate, a ceramic substrate, a quartzsubstrate or a glass substrate for displays or may be a semiconductor oninsulator (SOI) substrate. In the following description, a siliconsubstrate is used as an example.

The gates 116 are formed on the substrate 100. The gates 116 mayincluded in an n-channel metal oxide semiconductor (NMOS) transistor ora p-channel metal oxide semiconductor (PMOS) transistor. The gates 116may have a gate last structure or a replacement gate structure.Specifically, the first interlayer insulating film 121 includes anaperture 126, and the gateS 116 are disposed in the aperture 126.

The gates 116 may include, for example, a stack of a first metal layer115 and a second metal layer 110. The first metal layer 115 may beconformally formed along sidewalls and a bottom surface of the aperture126, and the second metal layer 110 may be formed on the first metallayer 115 to fill the aperture 126. The first metal layer 115 maycontain, e.g., TiN, and the second metal layer 110 may contain, e.g.,Al. In addition, if the gates 116 have a gate last structure, the firstinterlayer insulating film 121 may be lower than the gates 116.

The elevated source/drain 117 may be formed between the gates 116. Theelevated source/drain 117 may include a doped region 101 formed in thesubstrate 100 and an epitaxial layer 141 which contacts the doped region101. The epitaxial layer 141 may be a layer grown by an epitaxial methodusing the substrate 100 as a base.

The metal silicide 151 may be formed on the elevated source/drain 117.That is, a portion (in particular, the epitaxial layer 141) of theelevated source/drain 117 may include the metal silicide 151. A metalused in the metal silicide 151 may include at least one of Ni, Co, Pt,Ti, W, Hf, Yb, Tb, Dy, Er, Pd, and an alloy thereof. A contact hole 161passes through the first interlayer insulating film 121 and the secondinterlayer insulating film 122 and exposes at least part of the metalsilicide 151. A barrier layer 165 may be conformally formed alongsidesurfaces and a bottom surface of the contact hole 161, and the metalcontact 160 may be formed on the barrier layer 165 to fill the contacthole 161.

Referring to FIGS. 1 and 2, the elevated source/drain 117 may include aprotruding portion 141 a which protrudes further than a surface of thesubstrate 100 and covers both sides of the metal silicide 151. As shownin the drawings, the protruding portion 141 a may become narrower as thedistance from the surface of the substrate 100 increases. In addition,the protruding portion 141 a may cover more than half the verticallength (i.e., height) of the metal silicide 151. In FIG. 1, theprotruding portion 141 a covers the entire side surface 158 of the metalsilicide 151. However, the present invention is not limited thereto.

The metal silicide 151 may not be formed in at least part of a surface141 b of the elevated source/drain 117. That is, referring to FIG. 1,the elevated source/drain 117 may have an unsilicidized surface in aregion between the metal silicide 151 and the gates 116.

As shown in FIG. 2A, the metal silicide 151 may include a tip region159, a side surface 158, and an upper surface 156. The metal silicide151 may have a reversed cone shape, as shown in the drawings. Therefore,the tip region 159 may face downward (toward the substrate 100), and theupper surface 156 may face upward (away from the substrate 100). Inaddition, since the metal silicide 151 becomes wider from bottom to top,the side surface 158 may slope at a predetermined angle θ. Thepredetermined angle θ may be, but is not limited to, about 30 to about70 degrees. More specifically, the predetermined angle θ may be, but isnot limited to, about 40 to about 60 degrees. Also, the tip region 159of the metal silicide 151 may be located higher than the surface of thesubstrate 100. In some embodiments the tip region 159 is higher than agate oxide 120. In some embodiments, the tip region 159 is about 15 nmor less above the gate oxide 120.

As further shown in FIG. 2A and 2B, the metal silicide 151 cross-sectioncan define a lower profile 152 that is remote from the upper surface156. Furthermore, as shown in FIG. 2B, the metal silicide 151 in FIG. 2Ahighlights that the lower profile 152 of the metal silicide 151 has acurved cross-section and further shows that a central portion 159 of thecurved cross-section can be curved.

As further shown in FIG. 1, the metal silicide lower profile is at alevel in the elevated source/drain 117 that is elevated above a level ofa channel region that is associated with the directly adjacent gates116. In some embodiments according to the present invention, the metalsilicide lower profile 152 is at a level that is elevated above a levelof a gate oxide layers 120 that can be included in the directly adjacentgates 116. In still other embodiments according to the invention, adepth of the metal silicide lower profile 152 in the elevatedsource/drain region 117 is more than one half of the total thickness ofthe elevated source/drain region 117. In still other embodimentsaccording to the invention, the metal silicide lower profile 152 isabout 15 nm or less higher than the gate oxide layer included in thedirectly adjacent gates 116.

The metal silicide 151 and the elevated source/drain 117 may be formedusing processes described with reference to FIGS. 11 through 16. It willbe understood that, at least a portion of the elevated source/drain 117may be amorphized, and the amorphized elevated source/drain 1117 can betransformed into the metal silicide 151. Through these processes, themetal silicide 151 may take on the general shape of a reversed cone (toprovide a lower profile that has a curved cross-section), and the sidesurface 158 of the metal silicide 151 may slope at the predeterminedangle θ.

The amorphization process may be provided by a pre-amorphizationimplantation (PAI). Specifically, the amorphization process may be aprocess of implanting at least one of Si, Ge, Xe, and C as illustratedin FIG. 17. Therefore, the metal silicide 151 may contain at least oneof Si, Ge, Xe, and C. For example, the semiconductor device 1 may be anNMOS transistor, the epitaxial layer 141 may be Si, and Xe may be usedin the amorphization process. In this case, the metal silicide 151 maycontain Si and Xe. In another example, the semiconductor device 1 may bea PMOS transistor, the epitaxial layer 141 may be SiGe, and C may beused in the amorphization process. In this case, the metal silicide 151may contain Si, Ge, and C.

In some embodiments according to the invention, the semiconductor device1 can reduce the interfacial resistance between the elevatedsource/drain 117 and the metal silicide 151. This is because thereversed cone shape of the metal silicide 151 may provide a wide contactarea between the metal silicide 151 and the elevated source/drain 117.For example, if the reversed cone-shaped metal silicide 151 werecompared to a conventional flat (bar-shaped) metal silicide, it may beseen that the contact area between the reversed cone-shaped metalsilicide 151 and the elevated source/drain 117 is wider than a contactarea between the flat metal silicide and an elevated source/drain due tothe lower profile of the metal silicide 151 having a curvedcross-section. Also, the reversed cone shape of the metal silicide 151can promote the flow of current.

FIG. 3 is a cross-sectional view of a semiconductor device in someembodiments according to the present invention. FIG. 4 is a perspectiveview of a metal silicide 151 shown in FIG. 2. Referring to FIGS. 3 and4, in some embodiments according to the invention, the metal silicide151 may have a reversed cone shape, including an upper recess 151 awhich is recessed from an upper surface 156 of the reversed cone shapetoward the tip region 159. The shape of the lower profile of the metalsilicide 151, as seen in cross-section, may have be curved.

A vertical length L1 from a bottom of the upper recess 151 a to the tipregion 159 may be greater than a horizontal length L2 from the sidewallof the upper recess 151 a to a side surface 158. Here, each of thevertical length L1 and the horizontal length L2 is a length from aboundary of the upper recess 151 a. Since the metal silicide 151 extendsin a vertical direction, the vertical length L1 from the bottom of theupper recess 151 a to the tip region 159 may be longer than L2. Acentral portion of 159 of the metal silicide 151 can have a curvedprofile as shown in FIG. 4B.

The semiconductor device 2 may be a PMOS transistor. An elevatedsource/drain 102 may contain SiGe. A SiGe layer 142 may be formed in atrench formed in the substrate 100. The SiGe layer 142 may be sigma(E)-shaped. The SiGe layer 112 may apply compressive stress to the PMOStransistor, thereby increasing the mobility of carriers (holes) of thePMOS transistor. The SiGe layer 142 may be formed by an epitaxial methodto provide, an epitaxial layer 142 that contains the SiGe.

When at least one of Xe and C is used in an amorphization process, themetal silicide 152 may contain not only Si and Ge but also at least oneof Xe and C. A barrier layer 165 is formed on the metal silicide 151,and a metal contact 160 is formed on the barrier layer 165. The metalsilicide 151 may surround part of the barrier layer 165. Since the metalsilicide 151 includes the upper recess 151 a, the barrier layer 165 maybe formed in the upper recess 151 a.

As shown in FIGS. 4A and 4B, the metal silicide 151 may have a reversedcone shape, including an upper recess 151 a which is recessed from anupper surface 156 of the reversed cone shape toward the tip region 159.The shape of the lower profile of the metal silicide 151, as seen incross-section, may have be curved.

FIG. 5 is a cross-sectional view of a semiconductor device 3 in someembodiments according to the invention. FIGS. 6A and 6B are aperspective view and a cross-sectional view, respectively, of a metalsilicide 151 shown in FIG. 5.

Referring to FIGS. 5 and 6, the metal silicide 151 may have a reversedcone shape 151 a. In particular, the metal silicide 151 may include aconvex shaped top 151 b which protrudes upward from a horizontal plane156 of the reversed cone shape 151 a. As shown in the drawings, theconvex shaped top 151 b may be narrower than the width at the horizontalplane 156. The convex shaped top 151 b may become narrower from bottomto top.

An elevated source/drain 103 may contain a SiC layer 143 formed in atrench in a substrate 100. The SiC layer 143 may apply tensile stress toan NMOS transistor, thereby increasing the mobility of carriers(electrons) of the NMOS transistor. The SiC layer 143 may be formed byan epitaxial method. When at least one of Ge and Xe is used in anamorphization process, the metal silicide 151 may contain not only Siand C but also at least one of Ge and Xe.

As shown in FIGS. 6A and 6B, the metal silicide 151 may have a reversedcone shape, including a convex shaped top 151 b which protrudes upwardfrom a horizontal plane 156 of the reversed cone shape 151 a. The shapeof the lower profile of the metal silicide 151, as seen incross-section, may have be curved.

FIG. 7 is a cross-sectional view of a semiconductor device 4 in someembodiments according to the invention. In FIG. 7, a case where an NMOStransistor and a PMOS transistor are formed together is illustrated.Referring to FIG. 7, a first region I and a second region II are definedin a substrate 100.

A PMOS transistor may be formed in the first region I. The PMOStransistor may includes a first gate 111, a first elevated source/drain102 formed on both sides of the first gate 111, and a first metalsilicide 151 formed on the first elevated source/drain 102 and having areversed cone shape.

An NMOS transistor may be formed in the second region II. The NMOStransistor includes a second gate 211, a second elevated source/drain201 formed on both sides of the second gate 211, and a second metalsilicide 251 formed on the second elevated source/drain 201 and having areversed cone shape. The first metal silicide 151 and the second metalsilicide 251 may contain the same material. Here, the same material mayinclude at least one of Ge, Xe, and C.

For example, the first elevated source/drain 102 may contain SiGe, andthe second elevated source/drain 201 may contain Si. In this case, if Geis used in an amorphization process, Ge can be detected not only in thefirst metal silicide 151 but also in the second metal silicide 251.Alternatively, if Xe is used in the amorphization process, the firstmetal silicide 151 and the second metal silicide 251 may contain Xe.

As described above, the first metal silicide 151 may further include anupper recess in an upper surface of the reversed cone shape which isrecessed toward a tip region. In addition, the second silicide 251 mayfurther include a convex shaped top which protrudes upward from ahorizontal plane of the reversed cone shape, and the convex shaped topmay be narrower than the bottom surface. The convex shaped top maybecome narrower from bottom to top.

A side surface of the first metal silicide 151 may be at an angle θ1greater than an angle θ2 of a side surface of the second metal silicide251. That is, the side surface of the first metal silicide 151 of thePMOS transistor may be steeper than the side surface of the second metalsilicide 251 of the NMOS transistor.

As described above, the first elevated source/drain 102 may include aprotruding portion which protrudes further than a surface of thesubstrate 100 and covers both sides of the first metal silicide 151. Theprotruding portion may become narrower as the distance from the surfaceof the substrate 100 increases. The first metal silicide 151 may not beformed in at least part of a surface of the first elevated source/drain102. The tip region of the reversed cone shape of the first metalsilicide 152 is higher than a channel region of the first gate 111.

A tip region of the reversed cone shape of the second metal silicide 251may also be, but is not limited to, higher than the channel region ofthe second gate 211. Depending on the fabrication process, the tipregion of the second metal silicide 251 may be at about the same levelas the channel region or lower.

A first interlayer insulating film 121 including a first aperture 126and a second aperture 226 is further provided on the substrate 100. Thefirst gate 111 is formed in the first aperture 126, and the second gate211 is formed in the second aperture 226. In addition, the first gate111 includes a first metal layer 115 conformally formed along sidewallsand a bottom surface of the first aperture 126 and a second metal layer110 formed on the first metal layer 115 in the first aperture 126 tofill the first aperture 126. The second gate 211 includes a third metallayer 215 conformally formed along sidewalls and a bottom surface of thesecond aperture 226 and a fourth metal layer 210 formed on the thirdmetal layer 215 in the second aperture 226 to fill the second aperture226. As shown in the drawing, the first interlayer insulating film 121may be lower than the first gate 111 and the second gate 211. The NMOStransistor shown in FIGS. 5 and 6 may be formed in the second region II.That is, the NMOS transistor having the elevated source/drain 103 whichincludes the SiC epitaxial layer 143 may be formed.

FIG. 8 is a cross-sectional view of a semiconductor device 5 in someembodiments according to the invention. Referring to FIG. 8, a substrate100 includes a first region I, a second region II, and a third regionIII. The first region I and the second region II may be a memory regionand a logic region, respectively, and the third region II may be aperipheral region. The peripheral region may include, for example, aninput/output (I/O) region. The third region III may have a lower densityand a wider gap between elements than the first region I and the secondregion II.

A PMOS transistor and an NMOS transistor are formed in the first regionI and the second region II, respectively. The NMOS transistor shown inFIGS. 5 and 6 may be formed in the second region II. That is, the NMOStransistor having the elevated source/drain 103 which includes the SiCepitaxial layer 143 may be formed.

An epitaxial layer 341 may be formed on the substrate 100 of the thirdregion III, and a third metal silicide 351 having a reversed cone shapemay be formed on the epitaxial layer 341. The third metal silicide 351may be disposed between adjacent third gates 311. A third elevatedsource/drain 301 may be relatively wider than a first elevatedsource/drain 102 and a second elevated source/drain 201. In addition,the third metal silicide 351 may be relatively wider than a firstsilicide 151 and a second silicide 251.

FIGS. 9 and 10 are, respectively, a circuit diagram and a layout view ofa semiconductor device 6 in some embodiments according to the invention.The semiconductor devices 1 through 8 according to embodiments of thepresent invention are applicable to all devices using metal silicide.However, a static random access memory (SRAM) is illustrated as anexample in FIGS. 9 and 10.

Referring to FIG. 9, the semiconductor device 6 may include a pair ofinverters INV1 and INV2 connected in parallel between a power node Vccand a ground node Vss and a first transmission transistor T1 and asecond transmission transistor T2 connected respectively to output nodesof the inverters INV1 and INV2. The first transmission transistor T1 andthe second transmission transistor T2 may be connected to a bitline BLand a complementary bitline /BL, respectively. Gates of the firsttransmission transistor T1 and the second transmission transistor T2 maybe connected to wordlines WL1 and WL2, respectively.

The first inverter INV1 includes a first load transistor T5 and a firstdriving transistor T3 connected in series, and the second inverter INV2includes a second load transistor T6 and a second driving transistor T4connected in series. The first load transistor T5 and the second loadtransistor T6 may be PMOS transistors, and the first driving transistorT3 and the second driving transistor T4 may be NMOS transistors.

In addition, an input node of the first inverter INV1 is connected tothe output node of the second inverter INV2 (see a node NC2), and aninput node of the second inverter INV2 is connected to the output nodeof the first inverter INV1 (see a node NC1), such that the firstinverter INV1 and the second inverter INV2 can form one latch circuit.

Referring to FIGS. 9 and 10, reference numerals 410 and 412 indicateactive regions of the PMOS transistors, and reference numerals 414 and416 indicate active regions of the NMOS transistors. Reference numerals420 and 422 indicate gate electrodes of the first and second drivingtransistors T3 and T4, and reference numeral 430 indicates gateelectrodes of the first and second transmission transistors T1 and T2.Reference numeral 440 indicates a power line (Vcc line), referencenumeral 450 indicates a ground line (Vss line), and reference numeral460 indicates the bitline BL and the complementary bitline /BL. Here,reference numeral 490 indicates a metal contact. The metal silicides andmetal contacts of the semiconductor devices 1 through 8 according to theembodiments described above with reference to FIGS. 1 through 8 can beused.

FIGS. 11A through 16 are cross-sectional views illustrating methods offabricating the semiconductor device 2 in some embodiments according tothe invention. FIGS. 13B through 15B are enlarged cross-sectional viewsof FIGS. 13A through 15A. Referring to FIG. 11, a pair of transistorsare on a substrate 100. The transistors include gates 115/110 and anelevated source/drain 102, respectively, between the pair of transistors111 a/111 b. A first interlayer insulating film 121 covers the elevatedsource/drain 102. A second interlayer insulating film 122 is formed tocover the elevated source/drain 102 and the first interlayer insulatingfilm 121.

Referring to FIG. 12, a contact hole (or opening) 161 a is formed toexpose a surface of the elevated source/drain 102 by etching the firstinterlayer insulating film 121 and the second interlayer insulating film122. In some embodiments according to the invention, a mask pattern isformed on the second interlayer insulating film 122 and then dry-etched,thereby forming the contact hole 161 a.

Referring to FIGS. 13A and 13B, a radio frequency (RF) etching process198 is performed to reduce the size of the contact hole 161 b. The RFetching process 198 may use, for example, Ar+. The RF etching process198 can remove a natural oxide film formed on the elevated source/drain102. In addition, the RF etching process 198 can reduce the criticaldimension (CD) of a bottom surface of the contact hole 161 b. This isbecause the RF etching process 198 may cause etch by-products generatedfrom the elevated source/drain 102, the first interlayer insulating film121 and the second interlayer insulating film 122 to be re-deposited onsidewalls of the first interlayer insulating film 121 and the secondinterlayer insulating film 122. Accordingly, the RF etching in thecontact hole 161 b can change the shape at the bottom of the contacthole 161 b to provide curved sidewalls that curve at the bottom of thecontact hole 161 b toward the surface of the exposed elevatedsource/drain region 102 to promote the shape shown, for example, in FIG.13B.

Referring to FIGS. 14A and 14B, at least a portion 152 a of the elevatedsource/drain 102 is amorphized by an amorphization process 199.Specifically, the amorphization process 199 of at least a portion 195 ofthe elevated source/drain 102 may be provided by a pre-amorphizationimplant PAI. The amorphization process 199 may include a process ofimplanting at least one of Si, Ge, Xe, and C. As shown for example inFIG. 14B, the pre-amorphization implant can promote the formation of theamorphous portion 152 a to have a lower profile that is curved. It willbe understood that the lower profile of the pre-amorphization implant isremote from the surface of the directly adjacent elevated source/drainregion.

FIG. 17 is a graph illustrating exemplary thicknesses of amorphoussilicon layers formed in the elevated source/drain region versusthicknesses of metal silicide regions formed therein. According to FIG.17, the use of Si or Xe can promote the formation of thicker metalsilicides compared to the use of other impurities, such as C.

Referring to FIGS. 15A and 15B, a cleaning process may be performed.Specifically, the cleaning process may be performed in-situ. Thecleaning process can remove a natural oxide film formed on the elevatedsource/drain 102 and adjust the shape of the contact hole 161. Thecleaning process can be omitted.

Referring to FIG. 16, the amorphized elevated source/drain 102 issilicided with metal to form the metal silicide 151. The amorphizedportion induces a metal silicide 151 to grow more in a verticaldirection during the silicide process (see FIG. 16). That is, theamorphization portion can promote the formation of the metal silicide151 to follow the same general reversed cone shape as the amorphizedportion, so that a lower profile of the reversed cone shape can have acurved cross-section. The metal silicide 151 becomes wider from bottomto top. That is, the portion 151 a of the amorphized elevatedsource/drain 102 induces the metal silicide 151 to be generated in thevertical direction more than in the horizontal direction.

A metal layer can be formed on the amorphized elevated source/drain 102.For example, the metal layer may contain at least one of Ni, Co, Pt, Ti,W, Hf, Yb, Tb, Dy, Er, Pd, and an alloy thereof. The metal layer and theamorphized elevated source/drain 102 are made to react by a first heattreatment. For example, the first heat treatment may be performed at atemperature of about 200° C. to about 540° C. In addition, the firstheat treatment may use rapid thermal annealing (RTA). An unreactedportion of the metal layer is removed. Then, second heat treatment isperformed at a temperature higher than the temperature for the firstheat treatment. For example, the second heat treatment may be performedat a temperature of about 540° C. to about 800° C. The second heattreatment may also use RTA.

As shown in FIG. 16, the silicidation of the amorphized layer canpromote the growth of the metal silicide to have a lower profile (remotefrom the surface of the elevated source/drain) that is curved at acentral portion of the lower profile. Accordingly, in some embodimentsaccording to the invention, changing the shape of the contact hole at abottom thereof can promote the formation of the amorphous layer (inresponse to the pre-amorphization implant) which has a lower profilethat is curved which in turn can promote the formation of the metalsilicide also to have a curved cross-sectional profile, particularly ata central portion thereof.

Referring back to FIG. 3, a barrier layer 165 is conformally formedalong side surfaces and a bottom surface of the contact hole 161. Inaddition, a metal contact 160 is formed on the barrier layer 165 to fillthe contact hole 161.

While the inventive concept has been described with reference to exampleembodiments, it will be apparent to those skilled in the art thatvarious changes and modifications may be made without departing from thespirit and scope of the inventive concept. Therefore, it should beunderstood that the above embodiments are not limiting, butillustrative. Thus, the scope of the inventive concept is to bedetermined by the broadest permissible interpretation of the followingclaims and their equivalents, and shall not be restricted or limited bythe foregoing description.

1. A method of forming a semiconductor device comprising: forming anopening that exposes a surface of an elevated source/drain region;reducing a size of the opening; performing a pre-amorphization implant(PAI) into the elevated source/drain region, through the opening, toform an amorphized portion of the elevated source/drain region; andforming a metal-silicide from a metal and the amorphized portion.
 2. Themethod of claim 1 wherein performing the PAI comprises forming theamorphized portion to include a PAI lower profile that is remote fromthe surface, the PAI lower profile having a curved cross-section.
 3. Themethod of claim 2 wherein a central portion of the curved cross-sectionis curved.
 4. The method of claim 1 wherein forming a metal-silicidecomprises forming the metal-silicide to include a silicide lower profilethat is remote from the surface, the silicide lower profile having acurved cross-section.
 5. The method of claim 4 wherein a central portionof the curved cross-section is curved.
 6. The method of claim 4 whereinforming the metal-silicide comprises forming the silicide lower profileat a level that is equal to or higher than a gate oxide layer includedin a gate structure that is directly adjacent to the elevatedsource/drain region.
 7. The method of claim 6 wherein the level is about15 nm or less.
 8. The method of claim 4 wherein forming themetal-silicide comprises forming the silicide lower profile at a levelthat is elevated above a level of a channel region associated with atleast one directly adjacent gate structure.
 9. The method of claim 4wherein a depth of the silicide lower profile in the elevatedsource/drain region is more than one half of a total thickness of theelevated source/drain region.
 10. The method of claim 1 wherein reducinga size of the opening comprises reducing the size of the opening at abottom of the opening.
 11. The method of claim 1 wherein reducing a sizeof the opening comprises: changing a shape at a bottom of the opening toprovide curved side walls that curve at the bottom toward the surface ofthe elevated source/drain region.
 12. The method of claim 1 whereinreducing a size of the opening comprises: etching the surface of theelevated source/drain region to recess a level of the surface.
 13. Themethod of claim 1 wherein reducing a size of the opening comprises RFetching the elevated source/drain region and side walls of the opening.14. The method of claim 13 wherein performing the PAI comprises formingthe amorphized portion to include a PAI lower profile that is remotefrom the surface, the PAI lower profile having a curved cross-section.15. The method of claim 4 wherein the metal-silicide includes an upperrecess having a bottom and a side wall, wherein the bottom is separatedfrom a bottom of the silicide lower profile by a distance that isgreater than a distance by which the side wall of the recess isseparated from a side wall of the silicide lower profile.
 16. The methodof claim 4 wherein the metal-silicide further comprises a convex shapedtop, opposite the silicide lower profile.
 17. The method of claim 2wherein performing the PAI comprises implanting Xe into the elevatedsource/drain region to form the amorphized portion including the PAIlower profile, the amorphized portion having a total thickness of atleast about 100 Angstroms.
 18. The method of claim 2 wherein performingthe PAI comprises implanting Si into the elevated source/drain region toform the amorphized portion including the PAI lower profile, theamorphized portion having a total thickness of at least about 100Angstroms. 19-36. (canceled)